Accelerating materials discovery by high-throughput GIWAXS characterization of quasi-2D formamidinium metal halide perovskites

The intriguing functionalities of emerging quasi-two-dimensional (2D) metal halide perovskites (MHPs) have led to further exploration of this material class for sustainable and scalable optoelectronic applications. However, the chemical complexities in precursors – primarily determined by the 2D:3D compositional ratio – results in the uncontrolled phase heterogeneities in these materials, which compromises the optoelectronic performances. Yet, this phenomenon remains poorly understood due to the massive quasi-2D compositional space. To systematically explore the fundamental principles, herein, a high-throughput automated synthesis-characterization workflow is designed and implemented to formamidinium (FA)-based quasi-2D MHP system. It is revealed that the stable 3D-like phases, where the α-FAPbI3 surface is passivated by 2D spacer molecules, exclusively emerge at the compositional range (35-55% of FAPbI3) deviating from the stoichiometric considerations. Quantitative crystallographic study via high-throughput grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments integrated with automated peak analysis function, quickly reveals that the 3D-like phases are vertically aligned, facilitating vertical charge conduction that could be beneficial for optoelectronic applications. Together, our work clearly uncovers the optimal 2D:3D compositional range for complex quasi-2D MHP system realizing desired optoelectronic performances and stability. The automated experimental workflow significantly accelerates the materials discoveries and processing optimizations while providing fundamental insights into the complex materials systems.